The computer controlled internal combustion engine has an idling rotational speed control feed back system for maintaining a predetermined constant rotational idling speed. However, the idling control system operates unsatisfactorily due to an over-shoot effect which occurs during a short period after the engine is started. Therefore, the idling rotational speed become high. In this case, the increased rotational speed may exceed a predetermined value above which the operation of the fuel injector is stopped during the deceleration condition of the engine. As a result of this, a sharp decrease in idling rotational speed takes place, so that the idling operation becomes unstable.